On 16 May 1778, Amelia succeeded to the titles of 12th Baroness Darcy de Knayth and 9th Baroness Conyers in her own right, as the only surviving child of her father. Her right to the baronies of Darcy de Knayth and Conyers were eventually confirmed in 1798 (long after her death), and she also inherited the Portuguese countship of Mértola from him.

Lord and Lady Carmarthen divorced in May 1779. It was said that the marchioness had become over-friendly with John "Mad Jack" Byron (father of the poet, Lord Byron), who visited her at home in Grosvenor Square when her husband was absent, and that they had been having an affair.[3][4] Almost immediately after the divorce, she married Byron. They had one daughter, Augusta Leigh.

A year after the birth of her daughter by a year, in 1784, Amelia died[5] and the titles were inherited by her eldest son, George.